Electromagnetic Interference (EMI)

1 IBEX 2011 Speakers:David Gratton- Martek-Palm Beach, FLJohnny Lindstrom- Westport Shipyard, WAElectromagnetic Interference (EMI)Property of the NMEA. Shall not be copied or Overview EMI Troubleshooting EMI Prevention with Proper Cabling & Terminations Lightning Protection Corrosion GroundingProperty of the NMEA. Shall not be copied or Interference Unwanted Periodic signal /Energy One person s signal is another person s EMI. Interrupts, Obstructs, Degrades, or Limits Equipment PerformanceProperty of the NMEA. Shall not be copied or Interference Radiated Emissions RF Energy That Reaches Susceptible Equipment via Broadcast Conducted Emissions RF Energy That Reaches Susceptible Equipment via Common ConnectionsProperty of the NMEA.

2 Shall not be copied or Propagation Radiated Emissions Signals/Energy that Reaches Susceptible Equipment via Broadcast Radiated Power Decreases by Distance Squared Conducted Emissions Signals/Energy that Reaches Susceptible Equipment via Common Connections Combined Modes Signals/Energy that Propagates via Cable Connections that then Become signal RadiatorsProperty of the NMEA. Shall not be copied or Sources AC Units Alternators Battery Chargers Blower fans Engines Generators Inverters Propeller Shafts Radars WiringProperty of the NMEA. Shall not be copied or Recipients Electronic Compasses AV Systems Multifunction Displays Just about any Electronic DeviceProperty of the NMEA.

3 Shall not be copied or EMI Sources Trial-and-Error Process of Elimination Turn off All Equipment Except for Affected Device Turn on a Device and Check for Symptoms Repeat Until Interference Symptoms Return Additional Testing May Be Required to Determine If Interference Is Radiated or Conducted Interference May Be Radiated from Cables Connected to Interference SourceProperty of the NMEA. Shall not be copied or EMI Problems Layout and Space Planning Identify Potential EMI Radiation Sources Identify Potential EMI Conducted Sources Avoid Potential Hot SpotsVHFR adioAuto-pilotFRF TransmissionLineRudder FeedbackSignalParallel cable runs are not desirableProperty of the NMEA.

4 Shall not be copied or Is Application DependentInternal HighFrequencySignalDC PowerSupplyLeadsSignal OutputStageAC/RFOutputRF Outputto Antenna(AC signal Wave Form)Property of the NMEA. Shall not be copied or for Unintended Signals Objective: Block the signal Prevent signal Transmission on Cables Prevent signal Transmission through Enclosure Shielded Enclosure with Attached Ground Input and Output Cables Active Filters- usually BandPass or Notch Ferrites Best Practice is to attempt to solve problems within the offender rather than the offended .Property of the NMEA. Shall not be copied or as an EMI Suppressor Ferrites Composed of Ferrous Oxide and One or More Powdered Metals Composite Material Resists Imposed EMI Fields by Suppressing Electron Movement Variable Sensitivity to Frequency Lower Frequencies Pass without Significant Loss Above Resonant Frequency signal Becomes Coupled to Ferrite, Causing a High Impedance Increasing Turns Increases EffectivenessProperty of the NMEA.

5 Shall not be copied or GeometryProperty of the NMEA. Shall not be copied or for signal Cables Objective: Preserve signal on Cable; Prevent Radiation to Other Cables and Devices Balanced Signals Cancel Radiation Shielding Captures Radiation and Diverts signal to Ground (not applicable to coax). Find it with troubleshootingTypeCoverage Conductivity FlexibilityFoil100%poorpoorBraid85-95 %goodgoodProperty of the NMEA. Shall not be copied or Interference : Power cables Shielded Cables Connect One End of Shield to RF Ground Grounding Connect Case to RF Ground Better to Connect Source s Case Less Desirable to Connect Affected Device s Case Filters Install in Power Leads of offender first Ferrites Effective for Conducted and Radiated NoiseProperty of the NMEA.

6 Shall not be copied or Mitigation Relocate Cable Runs Relocate Equipment Displays Relocate Antennas Consider Antenna Radiation Patterns Consider Cable Lengths Avoid Multiples of Wave Length with power & data cables This is not an issue with coax cablesProperty of the NMEA. Shall not be copied or Loss CalculationsTotal Loss = Cable Loss + Connector Losses (Depends on Type)Cable Loss = Loss in dB per 100 ft. x Cable Length / 100 Connector Loss = Number of connectors x dB Property of the NMEA. Shall not be copied or SelectionConnector Ty p eMaximum FrequencyImpedancePermitted UsesUHF (PL-259)300 MHz50-OhmVHF, SSB, DGPS, Stereo BNC GHz50-OhmVHF, SSB, DGPS, Cell, GPS TNC GHz50-OhmVHF, SSB, DGPS, Cell, GPS, MINI-M N GHz50-OhmVHF, SSB, DGPS, Cell, GPS F GHz75-OhmTV, GPS Mini UHF GHz50-OhmCellSMA GHz50-OhmSAT PhoneSMB GHz50-OhmFME 200 MHz50-OhmVHF, SSB Property of the NMEA.

7 Shall not be copied or Bend RadiusCable TypeBend Radius (inches) to route coax cables using gentle S-curves (green) than tight right-angle turns (yellow) when Cables Attenuation Transmission Losses (dB per ft.) Connector Losses (dB) Impedance Mismatch (Avoidable) 50 - 75 Also affected by installation Cable Length Minimum Length Necessary (Most systems have no tuned length) Equipment Connections Match Application and Cable Type Extensions beware of the allowed lossCable SelectionRG58 URG8 XRG8 URG213 LMR240 LMR400 Nominal "1/4"13/32"13/32"1/4"13/32 Conductor (AWG)20161313159 Impedance(Ohms)505052505050 Impedance Match within 2 OhmsProperty of the NMEA.

8 Shall not be copied or Connections of Power Shields Connected to RF Ground System Effectiveness Dependent on Low Impedance to Ground Best Ground Path for High Frequency EMI signals is via Copper Foil #8 AWG Stranded Copper Wire AcceptableProperty of the NMEA. Shall not be copied or Strikes- GOOD LUCK! Direct Strike Direct Hit on a Part of the Vessel, Such as an Antenna or Mast. Conductive Strike Strike on a Utility Line and Conducted Aboard Through the AC Power Cord Inductive Strike Nearby Strike Causing a Large Magnetic Field, Which in Turn Induces a Voltage in the Vessel s Wiring There is no sure way to prevent damage from any type of to ABYC TE-4 Lightning Protection for more informationLightning Protection.

9 Two schools of thought Conductive and Inductive Commercially Available Surge Protection Products Direct Strikes Air Terminals Connected to Properly Sized Conductors, with Relatively Straight Paths to Ground Towers Grounded Port and StarboardRefer to ABYC TE-4 Lightning Protection for more informationProperty of the NMEA. Shall not be copied or Electrolysis Chemical and/or Electrochemical Change Due to Electric Current Galvanic Corrosion Corrosion from Electric Current Flow between Connected but Dissimilar Metals in the Same ElectrolyteRefer to ABYC E-11 AC & DC Electrical Systems on Boats for more informationOther Corrosion Sources Stray Current Corrosion Electric Current Flow Caused by an Outside Source.

10 (In a Marina). Velocity Corrosion Electric Current Flow Caused by Strong Water Currents Selective Corrosion Electric Current Flow Caused by Areas with Different Composition within the Same Alloy Oxygen Starvation Electric Current Flow Caused by Trapped Electrolytes Making Adjacent Surfaces More Positive to the Remaining Metal SurfaceRefer to ABYC E-11 AC & DC Electrical Systems on Boats for more informationTo Bond or Not to BondAge Old Debate! Decision Is Vessel Dependent Bonding Is Fairly Common in the Industry Aluminum Is Less Noble Than Almost Everything Else Always Isolate From Bonding System And/or Bond by Itself to a Sacrificial Anode Selected Especially for AluminumRefer to ABYC E-2 Cathodic Protection for more informationProperty of the NMEA.